> httrack www.somesite.com/update.html
> The file update.html have links point to a.html, b.html,
> c.html, ...
> respectively.
> And a.html link to a-1.html, a-2. html, b.html link to
> b-1.html, b-2.html,
> c.html link to c-1.html, c-2.html, ...
> Now, the site add a file a-10.html and add a link in 
a.html
> to point to
> this file.
> Other files (b.html, c.html ...) have no change.
> I want httrack action like this.
> Firstly, it find the file update.html was changed and
> download it.
> Sencondly, httrack access all links in update.html and 
find
> a.html was
> changed and
> b.html, c.html, ..., have no change. So httrack download
> a.html only.
> Thirdly and most importantly, httrack find files to update
> in a.html
> only, and ignore the links in b.html, c.html, ...., 
because
> b.html and  c.html have no change. 
> If httrack runs like the way discribed above, it will be 
faster.

But it won't work on most cases: what if b.html did not 
change, BUT b-1.html did? Limiting the update scan to 1 
does not work, unfortunately..